1. Field of the Invention
The invention relates to a method for the casting of rectangular billets from metal, in particular from steel, close to final dimensions and for the subsequent inline rolling out of the billet, with a material supply vessel, via the outlet nozzle of which the liquid metal is deposited onto the upper strand of a conveyor belt, on which it solidifies and is transferred to a roll stand for forming. The invention further relates to a corresponding device for carrying out the method.
2. Discussion of the Prior Art
Stahl und Eisen [Steel and Iron] 1986, page 65ff., discloses a method with a traveling mold for casting close to final dimensions, in which the steel is cast onto casting carriages moving horizontally. The casting carriages run on a rail, and at the end of the mold section the billet is transferred to a roller table, and the billet must have thoroughly solidified at the latest when it enters the first roll stand arranged downstream. This publication specifies the relationship between the casting speed and the effective mold length. There is no suggestion in this publication of changing the position of the material supply vessel during operation.
German reference DE 43 44 953 C2 discloses a method for casting a metal strip close to final dimensions on a belt-type casting device provided with a melt receiving vessel and with a conveyor belt, which lists method instructions and means for exerting influence on the spread of the metal melt on the conveyor belt. The arrangement of the casting vessel in relation to the conveyor belt cannot be changed in this case.
The object of the invention is to provide a method and a corresponding device in which simple design means ensure casting close to final dimensions and subsequent rolling of rectangular billets of high and uniform quality at any desired casting speed and with any desired billet thicknesses.
According to the invention, before the start of casting, the material supply vessel is set in a predeterminable position with respect to the longitudinal extent of the conveyor belt and therefore the point at which the liquid metal is deposited onto the conveyor belt is predetermined approximately. Furthermore, the conveying speed of the conveyor belt is set as a function of the desired rolling thickness and rolling speed of the roll stand. During operation, the position for thorough solidification and the temperature of the rolling stock are then used as control variables for the current position of the point at which the liquid material leaving the material supply vessel is deposited onto the conveyor belt.
The variable depositing of the melt onto the conveyor belt affords a simple and highly effective possibility for setting the mean temperature of the cast strip both at the end of the conveyor belt and at entry into the roll stand. In this case, the mean temperature comprises the average of the permissible temperature differences over the strip cross section of the cast strip.
The variable depositing point of the melt, specifically both approximate setting and the fine setting which is carried out during operation, makes it possible to set a special inlet temperature profile of the billet at entry into the rolling mill.
In addition to influence being exerted on the current position of the point at which the liquid metal leaving the material supply vessel is deposited onto the conveyor belt, further regulating subsystems are also advantageously used. Thus, it is proposed to detect the thickness of the material billet located on the conveyor belt and use said thickness for controlling the quantity flow of the liquid material leaving the material supply vessel. In a further advantageous procedure, the speed of the conveyor belt is detected and is used to control the quantity flow of the liquid material leaving the material supply vessel. Furthermore, the geodetic height of the metal located in the material supply vessel may be taken into account in the control of the quantity flow.
Moreover, in order to control the position of the material depositing point, it is proposed to take into account the discharge of heat from the metal billet located on the conveyor belt.
For carrying out the method, the material supply vessel has movement elements, by means of which it is capable of being moved horizontally, and at the same time coaxially to the major axis of the conveyor belt, in or opposite to the conveying direction of the billet. Furthermore, the material supply vessel is connected to an actuator which, for regulating purposes, is connected to a regulating means taking into account the thorough solidification of the billet and the temperature of the rolling stock and by means of which the position of the material supply vessel can be set as desired.
In an advantageous embodiment, the material supply vessel is equipped with wheels which run on rails. It is proposed, furthermore, to use sliding elements which match with a track.
In another advantageous embodiment, the movement elements are a thrust mechanism which is designed such that the mouth of the outlet nozzle of the material supply vessel can be guided at a constant distance from the upper strand of the conveyor belt over a defined region considered to be sufficient.
In another embodiment, piston/cylinder units are used, which are connected to a regulating means in such a way that, in the event of a horizontal movement of the material supply vessel, the mouth of the latter can be guided at a constant distance from the upper strand of the conveyor belt. In this case, the piston/cylinder units form the supports which are mounted at the corners of the material supply vessel.
A hydraulic piston/cylinder unit is proposed as an advantageous embodiment of an actuator for changing the horizontal position of the material supply vessel. In one embodiment, a piston/cylinder unit is provided, which is designed as a synchronous cylinder, one end of which is connected to the material supply vessel by a spacer rod.
In another advantageous embodiment, it is proposed that the position actuator be an electric drive which is connected to the material supply vessel by an endless belt.
It is proposed, furthermore, to arrange the position actuator and the material supply vessel on a stand and, in this case, to use the actuator for fine tuning and the stand, which has its own drive, for the approximate positioning of the material supply vessel.
Various forms of construction are proposed for the material supply vessel. In one embodiment, the material supply vessel is preceded by a ladle which is provided with a stopper rod or with a slide and which controls the inflow of the liquid metal. In another embodiment, the material supply vessel is designed as a vacuum vessel having a charging chamber, into which the melt is introduced.
In order to achieve reliably the desired material properties and the intended inlet temperature profile, in one embodiment of the invention a housing is provided which encases at least the free surfaces of the billet from the point at which the liquid metal is deposited onto the conveyor belt and during transport by the latter. This housing possesses a cover which is designed as a blind. This blind is connected at one end to the outlet nozzle of the material supply vessel and at the other end possesses a winding device. This housing is connected to a gas supply means, via which, in particular, inert gas is conveyed into the free space.
An example of the invention is presented in the accompanying drawing in which:
FIG. 1 shows a device for casting close to final dimensions, including the regulating means;
FIG. 2 shows the embodiment of the material supply vessel as a vacuum vessel; and
FIG. 3 shows a strip casting device with a housing.